Storage units and robotic storage/retrieval vehicles for a three-dimensional storage system

ABSTRACT

In combination, a storage unit storable within a three-dimensional storage system and a storage/retrieval vehicle navigable through the three-dimensional storage system to storage locations therein at which the storage unit is selectively storable and retrievable. The storage/retrieval vehicle comprises a frame conveyable through the three-dimensional storage system, a platform atop the frame for receipt of the storage unit on the platform, and a loading/unloading mechanism operable to load and unload the storage unit to and from the platform at four different sides thereof. The storage unit and the storage/retrieval vehicle are configured to enable unloading of the storage unit from the platform in any one of four different directions at four different respective sides of the vehicle regardless of an original orientation in which the storage unit was previously loaded onto the platform and without reorienting the storage unit from the original orientation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 U.S.C. 119(e) of U.S.Provisional Application No. 62/790,081, filed Jan. 9, 2019, the entiretyof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to automated storage andretrieval systems useful in order fulfillment environments.

BACKGROUND

Applicant's prior PCT application WO2016/172793, the entirety of whichis incorporated herein by reference, disclosed a goods-to-man storageand retrieval system employing a three-dimensional storage gridstructure in which a fleet of robotic storage/retrieval vehiclesnavigate a three-dimensional array of storage locations in whichrespective bins or other storage units are held. The storage/retrievalvehicles travel horizontally in two dimensions on both a gridded uppertrack layout disposed above the three-dimensional array of storagelocations, and a gridded lower track layout disposed at ground levelbelow the array of storage locations. The same storage/retrievalvehicles also traverse the structure in the third vertical dimensionthrough vertically upright shafts that join together the upper and lowertrack layouts. Each column of storage locations is neighboured by one ofthese upright shafts, whereby each and every storage location in thegrid is directly accessible by the storage/retrieval vehicles, which areequipped with rotatable turrets by which each robotic storage/retrievalvehicle can access any of the storage locations on all four sides of theshaft.

Continued development has led to numerous improvements in the systemdesign, including improvements to the robotic storage/retrieval vehiclesand the storage units compatible therewith, as documented in detail inthe following description and appended figures.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided, incombination, a storage unit storable within a three-dimensional storagesystem and a storage/retrieval vehicle navigable through saidthree-dimensional storage system to storage locations therein at whichsaid storage unit is selectively storable and retrievable, wherein saidstorage/retrieval vehicle comprises a frame conveyable through saidthree-dimensional storage system, a platform atop said frame for receiptof said storage unit on said platform, and a loading/unloading mechanismoperable to load and unload said storage unit to and from said platformat four different sides thereof, wherein said storage unit and saidstorage/retrieval vehicle are configured to enable unloading of thestorage unit from said platform in any one of four different directionsat four different respective sides of the vehicle regardless of anoriginal orientation in which said storage unit was previously loadedonto the platform and without reorienting said storage unit from saidoriginal orientation.

According to a second aspect of the invention, there is provided astorage/retrieval vehicle for use in a three-dimensional storage systemdelimiting storage locations at which respective storage units areselectively storable and retrievable, wherein said storage/retrievalvehicle comprises a frame conveyable through said three-dimensionalstorage system, a platform atop said frame for receipt of said storageunit on said platform, and a loading/unloading mechanism operable toload and unload said storage unit to and from said platform; wherein theloading/unloading mechanism comprises an extendable arm that isselectively extendable into a deployed position reaching outwardlybeyond a perimeter of the platform, and that comprises a movable shuttlethat is engageable with the storage unit and displaceable back and forthalong said extendable arm.

According to a third aspect of the invention, there is provided astorage unit for use in a three dimensional storage system navigable bya fleet of storage/retrieval vehicles each having a selectivelyextendable arm thereon by which the storage unit is engageable to unloadsaid storage unit from the vehicle into a storage location in saidthree-dimensional storage system and/or load said storage unit ontovehicle from said storage location, said storage unit comprising aprimary catch feature engageable by the extendable arms of thestorage/retrieval vehicles, wherein said primary catch features is acurved feature lying on a circular path.

According to a fourth aspect of the invention, there is provided amethod of handling a storage unit using a robotic storage/retrievalvehicle in a storage system having storage locations disposed onmultiple sides of travel paths through said storage system, said roboticstorage/retrieval vehicle having a loading/unloading mechanism that isadjustable between four different working states each operable to loadand unload said storage unit at a respective one of four different sidesof the vehicle, said method comprising, with said storage unit carriedon said robotic storage/retrieval vehicle, and while maintaining saidstorage unit in a static orientation and position on said roboticstorage/retrieval vehicle, adjusting the loading/unloading mechanismbetween two of the four different working states, thereby changing whichside of the vehicle said storage unit is offloadable therefrom withoutre-positioning or re-orienting said storage unit on said vehicle.

According to a fifth aspect of the invention, there is provided a methodof handling storage units using a robotic storage/retrieval vehicle in astorage system having storage locations in which said storage units arestored, said method comprising:

-   -   (a) attempting loading of a storage unit from a storage location        onto a platform of said robotic storage/retrieval vehicle using        a loading/unloading mechanism of said robotic storage/retrieval        vehicle;    -   (b) performing a load status check using a load status sensing        device to detect whether the storage unit has been properly        loaded onto said platform of said robotic storage/retrieval        vehicle;    -   (c) in response to detection by said load status sensing device        of a failure to fully load said storage unit onto said platform        of said robotic storage/retrieval vehicle, triggering an        automatic repositioning of the storage unit in the storage        location; and    -   (d) re-attempting loading of the storage unit onto the platform        of said robotic storage/retrieval vehicle using said        loading/unloading mechanism thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more preferred embodiments of the invention will now be describedin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a three-dimensional grid structure fromApplicant's aforementioned prior PCT application, in which athree-dimensional array of storage units are contained and through whicha fleet of robotic storage/retrieval vehicles can travel in threedimensions to access each said storage units.

FIG. 2 is a top right perspective view of a robotic storage/retrievalvehicle of the present invention.

FIG. 3 is a top right perspective view of the robotic storage/retrievalvehicle of FIG. 2 with a modular storage bin in a fully loaded positionthereon.

FIG. 4 is a top perspective view of a base module of the modular storagebin of FIG. 3.

FIG. 5 is a bottom perspective view of the base module of FIG. 4.

FIG. 6 is a bottom plan view of the base module of FIG. 4.

FIG. 7 is an overhead plan view of the base module of FIG. 4.

FIG. 8 is a cross-sectional view of the base module of FIG. 7 as viewedalong line A-A thereof.

FIGS. 9A through 9F are perspective views illustrating sequential stepsof a successful loading process pulling the modular storage bin into thefully loaded position on the robotic storage/retrieval vehicle.

FIGS. 10A through 10F are side elevational views illustrating thesequential steps of the successful loading process during extraction ofthe modular storage bin from a storage location in the three-dimensionalgrid structure of FIG. 1.

FIGS. 11 and 12 are closeup detailed views of FIGS. 10C and 10D,respectively.

FIGS. 13A through 13D illustrate sequential steps in a failed loadingprocess in which the storage bin is not properly engaged and is onlypartially loaded onto the robotic storage/retrieval vehicle, and FIGS.13E and 13F illustrate subsequent repositioning steps to unload thestorage bin back into the storage location in preparation for a repeatedloading attempt.

FIGS. 14A through 14D are schematic top plan views of the roboticstorage/retrieval vehicle of FIG. 2 with a loading/unloading mechanismthereof rotated into four different working positions, wherein brokenlines illustrate a circular catch channel in the underside of a storagebin carried on the vehicle to accommodate rotation of theloading/unloading mechanism relative to the storage unit.

FIGS. 15A through 15F illustrate sequential steps of an unloadingprocess pushing the modular storage bin off of the roboticstorage/retrieval vehicle into a selected storage location in thethree-dimensional grid structure.

DETAILED DESCRIPTION

FIG. 1 illustrates the three-dimensional grid structure 10 fromApplicant's aforementioned prior PCT application. A gridded upper tracklayout 12 resides in an elevated horizontal plane well above a matchingand aligned gridded lower track layout 14 situated in a lower horizontalplane closer to ground level. Between these aligned upper and lowertrack layouts is a three-dimensional array of storage locations, eachcapable of holding a respective storage unit 16 therein, for example inthe form of open-top or openable/closeable storage tray, bin or totecapable of holding any variety of goods therein. The storage locationsare arranged in vertical columns, in which storage locations of equalsquare footprint are aligned over one another. Each such storage column17 is neighboured by a vertically upright shaft 18 through which itsstorage locations are accessible. A fleet of robotic retrieval vehicles19 can horizontally traverse each track layouts in two dimensions, andcan traverse vertically between the two track layouts via the openshafts 18.

Each track layout features a set of X-direction rails 20 lying in theX-direction of the respective horizontal plane, and a set of Y-directionrails 22 perpendicularly crossing the X-direction rails in theY-direction of the same horizontal plane. The crossing rails define ahorizontal reference grid of the storage system, where each horizontalgrid row is delimited between an adjacent pair of the X-direction railsand each horizontal grid column is delimited between an adjacent pair ofthe Y-direction rails. Each intersection point between one of thehorizontal grid columns and one of the horizontal grid rows denotes theposition of a respective vertical storage column 17 or a respectiveupright shaft 18. In other words, each storage column 17 and each shaft18 resides at a respective Cartesian coordinate point of the referencegrid at a respective area bound between two of the X-direction rails andtwo of the Y-direction rails. Each such area bound between four rails ineither track layout is also referred to herein as a respective “spot” ofsaid track layout. The three-dimensional addressing of each storagelocation in the system is completed by the given vertical level at whichthe given storage location resides within the respective storage column17. That is, a three-dimensional address of each storage location isdictated by the horizontal grid row, horizontal grid column and verticalcolumn level of the storage location in the three-dimensional grid.

A respective upright frame member 24 spans vertically between the upperand lower track layouts at each intersection point between theX-direction and Y-direction rails, thereby cooperating with the trackrails to define a framework of the three-dimensional grid structure forcontaining and organizing the three-dimensional array of storage unitswithin this framework. As a result, each upright shaft 18 of thethree-dimensional storage array has four vertical frame members 24spanning the full height of the shaft at the four corners thereof. Eachframe member 24 has respective sets of rack teeth arranged in series inthe vertical Z-direction of the three-dimensional grid on two sides ofthe frame member. Each shaft thus has eight sets of rack teeth in total,with two sets at each corner of the shaft, which cooperate with eightpinion wheels on the robotic storage/retrieval vehicles 19 to enabletraversal of same between the upper and lower track layouts through theshafts 18 of the three-dimensional grid structure.

Each robotic storage/retrieval vehicle 19 has both round conveyancewheels for conveyance of the robotic storage/retrieval vehicle over theupper and lower track layouts in a track-riding mode, and toothed pinionwheels for traversal of the robotic storage/retrieval vehicle throughthe rack-equipped shafts in a shaft-traversing mode. Each pinion wheeland a respective conveyance wheel are part of a combined singular wheelunit, of which the entirety, or at least the conveyance wheel, isextendable in an outboard direction from the vehicle for use of theconveyance wheels in a track-riding mode on either track layout, andretractable in an inboard direction of the vehicle for use of the pinionwheels in a shaft-traversing mode engaging the pinion wheels with therack teeth of the upright frame members of a shaft.

The framework of the grid structure includes a set of shelving bracketsat each storage location to cooperatively form a shelf for the storageunit currently stored at said location, whereby any given storage unit16 can be removed from its storage location by one of the roboticretrieval vehicles 19 without disrupting the storage units above andbelow it in the same storage column. Likewise, this allows a storageunit to be returned to a prescribed location at any level in the array.

Though omitted in FIG. 1 to reveal the lower gridded track layout 14 atthe bottom of the three-dimensional grid, a number of working stationsare typically distributed around the perimeter of the lower griddedtrack layout to serve as destinations to which the robotic retrievalvehicles 19 deliver the storage units 16 pulled from the storagecolumns. Except for differences explicitly described herein, theframework of the three-dimensional grid structure, the working stations,the robotic storage/retrieval vehicles, the travel thereof horizontallyatop the upper and lower track layouts and vertically through theshafts, and their transition between the track-riding andshaft-traversing modes may be the same as described in Applicant'saforementioned prior PCT application, or in Applicant's U.S. provisionalpatent applications 62/682,691, filed Jun. 8, 2018, and 62/770,788,filed Nov. 22, 2018, the entireties of which are also incorporatedherein by reference.

FIG. 2 shows one of the robotic storage/retrieval vehicles 19 of thepresent invention, on which any storage unit 16 of the present inventionis receivable for transport thereof within the three-dimensional gridstructure to and from, and optionally through, the working stations. Inthe illustrated example, the storage unit to and from which smallerindividual items can be inserted and removed is an open-top bin 16,though as mentioned elsewhere herein above, an openable/closeable box ortote may alternatively be used. In other embodiments, the storage unitmay be the packaging of an individual item, as opposed to a containerfor storing multiple items therein. In other embodiments, where the griddimensions and working stations are of larger scale, a storage unit maybe a pallet on which one or items are received, whether one relativelylarge individual item, or a plurality of items. In the example ofmultiple palleted items, the items may be distributed among multiplecontainers (e.g. boxes, trays, bins or totes) placed or stacked on thepallet, with one or more items stored in each such container.

As disclosed in Applicant's aforementioned prior PCT application, eachrobotic storage/retrieval vehicle 19 features a frame or chassis 26 onwhich there are carried a set of four X-direction wheel units 28arranged in pairs on two opposing sides of the robotic storage/retrievalvehicle, and a set of four Y-direction wheel units 30 arranged in pairson the other two opposing sides of the robotic storage/retrievalvehicle. Each X-direction wheel unit 28 resides just around the cornerfrom a respective Y-direction wheel unit 30 at a neighbouring side ofthe vehicle frame 16. The details of the pinion and conveyance teeth andassociated drive componentry are omitted for illustrative simplicity,and may be identical to those disclosed in Applicant's aforementionedprior PCT application. Atop the frame 26 is disposed an upper supportplatform 32 on which the storage unit 16 is receivable for carryingthereof by the robotic storage/retrieval vehicle 19. The illustratedplatform features a rotatable turret 34 surrounded by a stationary outerdeck surface 36, the outer boundaries of which denote the square outerperimeter 37 of the platform 32.

The turret has a linearly extendable/retractable arm 38 mounted in adiametric slot of the turret and movably supported therein for linearmovement into and out of a deployed position extending outwardly fromthe outer circumference of the turret at an arm-deployment point 34 adenoted by one end of the diametric slot. FIG. 2 shows the arm 38 in afully retracted position contained entirely within the diametric slot soas not to project beyond the outer circumference of the turret. Theextendable/retractable function of the arm 38, together with therotatable function of the turret, allows pulling of storage units ontothe support platform, and pushing of storage units off the supportplatform, at all four sides of the robotic storage/retrieval vehicle.That is, the turret is rotatable into four different working positions,shown in FIG. 14. In each working position, the arm-deployment point 34a on the turret circumference points toward a respective perimeter sideof the platform to enable selective extension of the arm 28 outwardlyfrom that side of the platform to interact with a storage unit situatedon that side of the vehicle. Accordingly, each vehicle can access astorage unit on any side of any shaft in the three-dimensional gridstructure since the arm can be extended to any of the vehicle's foursides.

The turret 34 and surrounding deck surface 36 of the platformcollectively define a square landing area atop which the storage unit isseated when carried on the upper platform robotic storage/retrievalvehicle 14. This landing area is equal or nearly equal in size and shapeto the underside of each storage unit in the three-dimensional gridstructure. This is demonstrated by FIG. 3, where the fully and properlyseated position of the storage unit can be seen to occupy a full or nearentirety of the landing area without overhanging the outer perimeter ofthe platform. Accordingly, in its properly seated position on thelanding area, the entire footprint of the storage unit resides withinthe outer perimeter of the platform or landing area.

For the purpose of ensuring that the storage unit is fully received andproperly aligned on the landing area of the robotic storage/retrievalvehicle, the upper support platform 32 has a set of load status sensors40 situated in close proximity to the outer perimeter thereof at spacedapart positions along said perimeter. In the illustrated example, theload sensors are optical sensors recessed in the deck surface 36 of thelanding area, and provided in a quantity of four, each positionedproximate a respective one of the four outer corners of the squarelanding area. As part of a loading routine pulling a storage unit ontothe robotic storage/retrieval vehicle from a storage location in thethree-dimensional grid using retraction of the extendable/retractablearm, a computer processor communicably connected to the load statussensors, for example a local process on-board the vehicle, checks thestatus of the four load status sensors for detected presence of theunderside of the storage unit above the sensor. A positive detectionsignal from all four load status sensors thus confirms the presence ofthe storage unit at all four corners of the landing area, therebyconfirming that the storage unit is fully received on the landing areaand is in properly squared alignment thereon.

One embodiment uses reflective optical sensors for load statusdetection, where light energy transmitted by an optical beam emitter ofthe sensor is reflected off the underside of the storage unit back to anoptical receiver of the sensor when the storage unit is presentthereover, thus successfully determining said presence. Time of flightcalculation (i.e difference in time between emission of an optical pulseand detection of the reflected optical pulse) may be used todifferentiate between reflection off the underside of a storage binseated on the landing area of the robotic storage/retrieval vehicleversus reflection off another surface situated further away from thesensor. It will be appreciated that sensor types other than opticalsensors may be employed, for example including limit switchesmechanically actuated by contact with the underside of the storage unit,or magnetic sensors actuated by presence of cooperating magneticelements emitting detectable magnetic fields at the underside of thestorage unit. However, optical sensors may be preferable to avoid movingparts or need for magnetic integration or other specializedconfiguration of the storage units.

Referring to FIG. 3, the storage unit 16 in the illustrated embodimentis a modular storage unit composed at least of a base module 42, andoptionally having one or more wall modules 44 stacked atop the basemodule to increase an overall height of the modular storage unit 16. Thebase module 42 is the part of the storage unit that is seated on theshelving brackets of the three-dimensional grid structure when disposedin a respective storage location therein, and likewise is the part ofthe storage unit that is seated on the platform 32 of the roboticstorage/retrieval vehicle 19 when carried thereon for conveyance to orfrom a storage location in the grid structure.

Turning to FIGS. 4 through 8, the base module 42 features a horizontalfloor panel 46 of generally equal square shape and size to the platformlanding area of the robotic storage/retrieval vehicle 19, and a set offour vertical side walls 48 standing perpendicularly upright from thesquare floor panel 48 at the four perimeter edges thereof. A height ofeach side wall 48 is notably lesser than the width of the floor panel46, whereby the base module 42 has a tray-like shape delimiting arelatively shallow interior space between the four side walls 48 abovethe floor panel 46. Each optional wall module 44 is bottomless andtopless, consisting solely of a set of four rectangular vertical sidewalls 54 that preferably each have a handle opening 56 therein, and thatare laid out on respective sides of a square area matching that of thebase module's floor panel. Accordingly, in a stacked position atop thebase module, the four side walls 54 of each wall module reside inaligned relation over the side walls 48 of the base module. Accordingly,the wall modules serve as wall extensions to the base module to increasethe height of the interior space of the modular storage unit, thustransforming the modular storage unit from a relatively shallow trayinto a tote or bin whose deeper interior is delimited by the extendedwalls of the modular assembly.

The topside of the floor panel 46 of the base module defines a floorarea of the interior space of the storage unit, and it is on this floorarea that items are placeable within the confines of the side walls forstorage of such items inside the storage unit. The underside of thefloor panel 46 defines the underside of the overall storage unit, and itis here that a number of catch features are defined for cooperation witha catch member on the extendable/retractable arm of thestorage/retrieval vehicle 19 to enable loading and unloading of thestorage unit 16 to and from the storage/retrieval vehicle, as describedin more detail below. Though the illustrated embodiment employs amodular storage unit, non-modular single-piece storage units maynonetheless employ the same or similar catch features as those disclosedbelow to provide the same co-operable functionality with thestorage/retrieval vehicles of the type described herein.

A primary catch feature in the underside of the storage unit is acircular open-bottom channel 58 that follows a 360-degree circular patharound a center point 60 of the floor panel at an intermediate radialdistance between this center point 60 and the outer perimeter of thefloor panel 46. This circular catch channel 58 can seen from the openbottom side 58 a thereof in the bottom plan view of FIG. 6, and from theclosed top side 58 b thereof in the top plan view of FIG. 7. In FIG. 7,the channel is identifiable from the top due to a perforated skeletal orweb-like structure of the floor panel in the illustrated embodiment,where the floor panel features apertures or openings 61 laid out in aseries of circular arrays that are centered around the floor panel'scenter point. The closed top side 58 b of the channel 58 is thus visiblein FIG. 7 as a continuous ring centered on the center point 60 of thefloor panel and residing at an intermediate radial distance between thecenter point 60 and the floor area's outer perimeter. In otherembodiments where the topside of the floor is of a non-perforated, orless-perforated, structure, the open-bottom channel 58 in the undersideof the floor panel may not be identifiable at the topside thereof.

With reference to the bottom views in FIGS. 5 and 6, in the web-likefloor panel of the illustrated embodiment, inner radial ribs 62 of thefloor panel 46 radiate outward from the center point 60 thereof to aninside wall 63 of the channel 58. Outer radial ribs 64, some of whichare aligned with the inner radial ribs, continue from an outside wall 66of the channel 58 to the outer perimeter of the floor. At this outerperimeter of the floor panel, the outer radial ribs connect with thebase module side walls 48 at the bottom ends thereof. As shown, radialbraces 68 of lesser height than the radial ribs may interconnect theinside and outside walls 63, 66 of the channel 58 at angularly spacedpositions therearound, for example at angular intervals matching thoseat which the inner radial ribs are spaced from one another around thecenter point of the floor panel. The bottom ends of these braces 68terminate at a greater elevation than the bottom ends of the radial ribs62, 64 so that a lower half of the channel is entirely open anduninterrupted in its circular path around the center of the floor panel.The bottom ends of the radial ribs 62, 64 all reside coplanar with oneanother, thus defining a lowermost plane of the storage unit form whichthe catch channel 58 is recessed upwardly to create a continuouscircular slot in which a catch member of the vehicle's extendable armcan be received to enable loading and unloading of the storage bin toand from the vehicle, as described in more detail below.

Just inside the outer perimeter of the floor panel 46 at each of thefour sides thereof, the underside of the storage unit features arespective secondary catch recess 70 that is likewise recessed upwardlyfrom the lowermost plane of the storage unit for selective engagement ofthis catch recess 70 by the catch member of the extension arm shuttle ofthe storage/retrieval vehicle. However, each catch recess is arelatively small rectangular slot or cavity, unlike the much largercatch channel spanning a substantial circumferential distance around thecenter the of the floor panel. Each catch recess 70 is located mid-wayalong the respective perimeter side of the storage unit floor panel 48,thus interrupting a respective one of the outer radial ribs 64 at ornear an outer end thereof where this rib perpendicularly intersects therespective side wall 48 of the storage unit at a midpoint thereof. Thefour secondary catch recesses 70 are thus disposed at ninety-degreeintervals from one another around the center point of the storage unitfloor just inside the outer perimeter of the storage unit.

In addition to the catch channel 58 and catch recesses 70, the undersideof the storage unit features four bosses 72 disposed just inside theouter perimeter of the floor area at the four corners thereof. Each boss72 forms a cylindrical enlargement on a respective diagonal outer ribthat intersects the square outer perimeter of the floor panel at arespective corner thereof. The bottom ends of these bosses 72 arecoterminous with the bottom ends of the radial ribs to form enlargedsolid surface areas at the lowermost plane of the storage unit foralignment with and detection by the optical sensors 40 at the corners ofthe vehicle platform 32 when the storage unit is properly loaded in analigned position thereon. In embodiments where the floor panel 46 is ofsolid or less perforated structure, the underside of the floor panelmay, except for the circular primary catch channel 58 and four secondarycatch recesses 70, be a continuous solid surface spanninguninterruptedly from the catch channel 58 to outer corners of the floorpanel, thereby omitting the need for the bosses 72 of the skeletal orweb-like floor structure of the illustrated embodiment.

The extendable/retractable arm 38 of the storage/retrieval vehicle has amovable shuttle 74 thereon. The shuttle 74 features a horizontal baseplate 76 and a raised ridge-like catch member 78 standing verticallyupward therefrom in a cross-wise orientation lying perpendicular to thelongitudinal direction of the extendable/retractable arm 38 (i.e. thedirection in which the arm is elongated and linearly extendable andretractable from the rotatable turret 34). The arm 38 and shuttle formsparts of a loading/unloading mechanism by which the storage/retrievalvehicle can cooperate with the primary circular catch channel 58 of thestorage unit 16 to load and unload the storage unit to and from thevehicle 19, and also by which the secondary catch recesses 70 are usableas a backup should the loading mechanism fail to engage the primarycircular catch channel 58. The shuttle 74 is movable back and forthrelative to the arm 38 at a topside thereof in the longitudinaldirection, for example via a closed-loop belt 75 or chain entrainedabout a motorized pulley or sprocket set carried on same arm 38. Anupper run of said belt 75 or chain runs longitudinally of the arm 38 atthe topside thereof carries the shuttle 74 thereon, whereby drivenrevolution of the belt or chain in opposing direction drives linearmovement of the shuffle 74 back and forth in the longitudinal directionof the arm 38 at the topside thereof.

Having described the structure of the vehicle's loading/unloadingmechanism and the corresponding catch features on the storage unit,attention is now turned to cooperation therebetween to effect loadingand unloading of the storage unit to and from the vehicle. FIGS. 9 and10 illustrating successful performance of a normal loading routinepulling the storage unit onto the platform of the roboticstorage/retrieval vehicle, for example from a storage location insidethe three-dimensional grid structure of FIG. 1. FIG. 9 shows the processin perspective view with the vehicle and storage unit isolated from thethree-dimensional grid structure, while FIG. 10 shows a side view withselect elements of the grid structure present for contextual purposes.

With reference to FIG. 10A, the robotic storage/retrieval vehicle 19first travels vertically through a shaft 18 of the grid structure, forexample downwardly from the upper gridded track layout, via engagementof the pinion wheels of the robotic storage/retrieval vehicle with rackteeth on the frame members 24 at the corners of the shaft 18, until therobotic storage/retrieval vehicle reaches an initial pre-loadingposition in which the topside of the vehicle platform 32 resides at anelevation shortly below the lowermost plane of the targeted storage unit16. If not already situated in the particular working position pointingthe arm-deployment point 34 a toward the front side of the vehicle thatfaces the storage column 17 in which the targeted storage unit 16 iscurrently shelved at a given storage location, then the turret 34 isrotated into this particular forward-facing position working position.

It will be appreciated that the terms front/forward/rear/rearward areused relative to the storage location to or from which a storage unit isbeing deposited or extracted, and not in absolute terms to refer tospecific sides of the vehicle. For example, when interacting with astorage location on a north side of a given shaft 18 of the gridstructure in which the vehicle 19 currently resides, the “front side” ofthe vehicle refers to the north-facing side thereof. On the other hand,when interacting with a storage location on a south side of a shaft,whether the same shaft or otherwise, the “front side” of the vehiclerefers to the south-facing side thereof. The vehicle's orientation inthree-dimensional space never changes in its travel through thethree-dimensional grid structure, so the north-facing side always facesnorth, the south-facing side always faces south, etc.

Turning to FIG. 10B, the vehicle extends its arm 38 forwardly out fromthe turret at this front side of the vehicle, thus reaching the arm 38forwardly through the open side of the shaft 18 into the storage column17 at an elevation closely beneath the currently shelved storage unit16. During this deployment of the arm 38, the shuttle 74 is displacedlongitudinally forward on the deployed arm toward a distal end 38 athereof furthest from the turret, as shown in FIG. 11. Such extension ofthe arm and forward displacement of the shuttle is performed until theshuttle reaches a predetermined point on the arm 38 that is known todirectly underlie the primary circular catch channel 58 in the undersideof the storage unit 16, provided that the storage unit is seated in aproperly shelved position in its current storage location, e.g. abuttedagainst an appropriate stop at the far end of the shelf opposite theshaft 18. FIGS. 10C and 11 represent this stage in the loading routine,where the deployed state of the arm 38 and shuttle 74 have placed thecatch member 78 in alignment under the primary circular catch channel 58in the underside of the storage unit 16. The robotic storage/retrievalvehicle 19 is driven slightly upwardly by its pinion wheel engagementwith the rack-toothed frame members 24 at the corners of the shaft 18 toraise the catch member 78 of the shuttle 74 up into engagement with theprimary circular catch channel 58, as represented in FIGS. 10D and 12.

At this point, the deployed arm 38 is retracted, whereby the storageunit 16 is pulled toward the vehicle 19 by the catch member 78 until theshuttle 74 reaches a check position Pc situated inwardly of theperimeter of the vehicle platform 32, thus having pulled the nearestside of the storage unit 16 onto the platform 32 of the vehicle 19, asshown in FIG. 10E. At this point, the on-board processor of the roboticstorage retrieval vehicle queries the status of the load sensors 40 tocheck that the two load sensors adjacent the front side of the vehicleboth indicate a positive “load detected” status confirming the presenceof the storage unit 16 overtop of these two front load sensors. If theresult of this query is positive, then the processor has confirmedsuccessful pulling of the storage unit partially onto the vehicleplatform 32.

In response, the processor triggers further displacement of the shuttle72 in the rearward direction away from the distal end 38 a of the arm38, along with further retraction of the arm 38 if not already fullyretracted into the rotatable turret 34. With reference to FIG. 10F, theshuttle is driven rearwardly on the fully retracted arm 38 until itpasses the center point of the vehicle platform 32 and reaches apredetermined park position Pp that's rearwardly spaced from theplatform center point by a distance equal to the radial distance fromthe center point of the storage unit floor panel to the primary circularcatch channel 58 therein. Accordingly, this park position Pp of theshuttle corresponds to a fully loaded position of the storage unit 16 onthe vehicle platform 32, as shown in FIG. 10F. Upon arrival of theshuttle at the park position Pp, the vehicle processor queries the fourload sensors 40 again to check for a positive “load detected” statusfrom all four load sensors, thereby confirming that the storage binreached the fully loaded d position and is properly aligned atop thevehicle platform 32.

The forgoing example illustrated in FIGS. 9 and 10 reflects successfulcompletion of a normal loading process, where the catch member 78 of thevehicle's loading/unloading mechanism properly engages the primarycircular catch channel 58 of the storage unit, in which case no relianceis made on the secondary catch recesses 70 of the storage unit. On theother hand, FIG. 13 demonstrates how reliance can be made on thesecondary catch recesses 70 to enable a successful second loadingattempt should engagement of the primary circular catch channel failduring a first loading attempt.

FIG. 13A illustrates the same arm and shuttle retraction step as FIG.10D, but in an instance where the catch member 78 of the movable shuttle74 failed to engage in the primary circular catch channel 58 in thepreceding step of FIG. 10C. As a result, in FIG. 13A, the initialretraction of the arm 38 and shuttle 74 from their forwardly deployedpositions doesn't pull the storage unit 16 outwardly from its shelvedposition in the storage location of the grid structure. Instead, thecatch member 78 on the retracting arm and shuttle rides along theunderside of the storage unit 16 toward the secondary catch recess 70adjacent the side of the storage unit 16 that is nearest the vehicle 19and faces into the shaft 18. As shown in FIG. 13B, once the movingshuttle 74 arrives at this nearest vehicle-facing side of the storageunit, the secondary catch recess 70 at this nearest side of the storageunit falls onto the catch member 78 of the shuttle 74, thus achievingengagement of between the loading mechanism of the vehicle and thestorage unit 16 despite the initial failed engagement at the primarycircular catch channel 58.

As shown in FIG. 13C rearward retraction of the arm 38 and shuttle 74 iscontinued until the shuttle 74 reaches the check point Pc, thus havingpulled the nearest side of the storage unit 16 onto the vehicle platform19 into a position where a leading portion of storage unit overlies thetwo load status sensors adjacent the front side of the vehicle. Furtherretraction of the shuttle 74 is continued in the same manner asdescribed above for the normal successful loading process, thus bringingthe shuttle into the park position Pp near the opposing rear side of thevehicle. However, because the pulling of the storage bin 16 wasperformed at the secondary catch recess 70 near the outer perimeter ofthe storage unit floor, the storage bin stops short of the second pairof load sensors at the rear side of the platform. Accordingly, query ofthe load sensors upon arrival of the shuttle at the park position Ppresults in a positive “load detected” status at only the two frontsensors, and a negative “no load” status at the two rear sensors. Thisdetection by the processor of a negative “no load” status at the rearsensors indicates that there has been a failure to fully load thestorage unit 16 onto the vehicle platform 32, as shown in FIG. 13D, butthe positive “load detected” status by a partial subset of the loadsensors (i.e. the two front sensors) confirms that a partially loadedstatus was obtain, from which it is concluded that the secondary catchrecess 70 was successfully engaged.

In response to this detection that the storage unit wasn't fully loaded,but that the secondary catch recess 70 was engaged, the processinitiates a corrective operation intended to offload the partiallyloaded storage unit from the vehicle back into the storage location, andto re-position the storage unit in a properly shelved condition thereinbefore re-attempting another loading process. To start, the processorinitiates forward displacement of the shuttle 74 and forward extensionof the arm 38 into the storage column 17, as shown in FIG. 13E, thuspushing the partially loaded storage unit 16 back into the storagelocation via the catch member's engaged position inside the secondarycatch recess 70 of the storage unit. The forward travel of the shuttlefrom the check position Pc during this forward re-deployment of the armand shuttle is selected to equal the known distance from which thecurrent engaged secondary catch recess 70 should reside from the stop atthe far end of the shelf when the storage unit is fully and properlyshelved. Accordingly, the forward re-deployment of the arm and shuttlepushes the storage unit into a fully shelved position in the storagelocation.

At this point, as shown in FIG. 13F, the robotic storage/retrievalvehicle 19 in the shaft 18 then lowers itself slightly downward viaoperation of its pinion wheels in order to drop the catch member 78 ofthe shuttle 74 out of engagement with the secondary catch recess 70 ofthe storage unit 16, thus placing the shuttle 74 and arm 38 beneath thestorage unit 16 in an unengaged position spaced slightly therebelow. Atthis point, the normal loading procedure steps illustrated in FIGS. 10Bthrough 10F can be repeated to reattempt full and proper extraction andloading of the storage unit from the storage location using the primarycircular catch channel 58.

The secondary catch recesses 70 and described cooperation with theloading mechanism thus provides a redundant catch arrangement by which afirst failed extraction and loading of the storage unit from thelocation onto the vehicle, for example due to vibrational shifting orother misalignment of the storage unit 16 from a properly shelvedposition in the storage location, can be corrected by partiallyextracting the storage unit 16 from the storage location, and then fullyre-inserting the partially extracted storage unit back into the storagelocation to attain proper alignment on the shelving, and thus enablingenable successful full extraction and loading in a repeated second orattempt to engage the primary circular catch channel. The processor maybe configured to perform multiple repositioning operations and loadingre-attempts before concluding that further attempts aren't likely tosucceed, and instead triggering the transmission of a wireless alarmsignal to a central computerized control system responsible forcontrolling and monitoring the vehicle fleet so that human interventioncan be initiated to diagnose and resolve the source of the loadingcomplication.

The inclusion of a redundant catch feature like the perimeter-adjacentcatch recesses 70 of the illustrated embodiment may be exploitedregardless of whether the primary catch feature is a circular catchchannel 58 like that of the illustrated embodiment. On the other hand,the use of a circular catch channel has notable benefit, as demonstratedby FIG. 14, in which the platform of a storage retrieval vehicle isschematically illustrated in top plan view, and the primary circularcatch channel 58 of a storage unit seated on the vehicle platform in afully loaded and aligned position is shown in broken lines.

The topside of the turret 34 resides in slightly recessed elevationrelative to the surrounding deck surface 36 of the vehicle platform 32,whereby the underside of the storage unit 16 carried on the vehicleplatform 32 sits in direct contact only with the slightly higher decksurface 36, and not with the topside of the rotating turret 38. Of theextendable/retractable arm 38 and the movable shuttle 74 carriedthereon, only the catch member 78 of the shuttle 74 reaches and exceedsthe elevation of the deck surface 36. The center point of the storageunit's floor panel 46, around which the primary circular catch channel58 is centered, is coincident with the center point of the vehicleplatform 32, and both of these center points are coincident with thevertical rotation axis AR of the turret 38. The circular catch channel58 thus allows rotation of the turret 34 to be performed while thestorage unit remains statically seated in a stationary position on thedeck surface 36, as the catch member 78, normally maintained in theparked position Pp on the retracted arm 38 of the turret 34, can simplytravel through the circular catch channel 58 on a revolutionary patharound the rotational axis AR during the rotation of the turret FIG. 14illustrates rotation of the turret through a full 360-degrees, therebydemonstrating attainment of the any of the four different workingpositions of the turret, without the seated storage unit 16 ever havingto be removed from, or reoriented on, the vehicle platform 32.

This enables unloading of a vehicle-carried storage unit into anyavailable storage space on any side of any shaft of thethree-dimensional storage grid regardless of what orientation thestorage unit was originally placed on the vehicle. Accordingly, avehicle having retrieved a storage unit from a north side of one shaftcan subsequently re-stock that storage unit at any storage location onany side of any shaft, whether on the north, south, east or west sidethereof, without the storage unit ever having to be removed from, orre-oriented on, the vehicle. In the illustrated embodiment, the circularchannel spans a full 360-degrees, thus enabling the turret to rotateinto any of its four different working positions in either directionabout the turret's rotational axis. While this full 360-degree span ispreferable, it will be appreciated that a 270-degree span would besufficient to accommodate the catch member of the shuttle in any of theturret's four working positions, though this would require knowledge ofthe orientation in which the storage unit resides on the vehicle inorder to limit movement of the catch member to the angular regionspanned around the turret's rotational axis by catch channel of thecurrently-carried storage unit. In the preferred 360-degree embodiment,the orientation in which a storage unit is placed or loaded onto thevehicle is of no consequence.

Turning to FIG. 15, the process of unloading a storage unit 16 from thevehicle 19 into a storage location in the grid structure is basically areversal of the normal loading procedure described with reference toFIG. 10. Referring to FIG. 15A, the vehicle 19 first travels verticallythrough a shaft 18 of the grid structure, for example downwardly throughthe shaft from the gridded upper track layout, via engagement of thepinion wheels of the vehicle with rack teeth on the frame members 24 atthe corners of the shaft 18, until the robot reaches an initialpre-unloading position in which the topside of the vehicle platform 32resides at an elevation slightly above the shelving brackets of thestorage location for which the storage unit is destined. If not alreadyin the forward-facing working position, then the turret 34 is rotatedbeneath the stationary storage unit into this forward-facing workingposition.

With reference to FIGS. 15B and 15C, the arm 38 is extended forwardlyfrom the turret 34 into the storage column 17 and the movable shuttle isdisplaced forwardly along the arm. Since the catch member 78 shuttle 74remains engaged in the primary circular catch channel 58 of the storageunit from the time the storage unit was first loaded or placed on thevehicle, this forward movement of the shuttle 74 from its parkedposition Pp toward and into the targeted storage location in the storagecolumn 17 pushes the storage unit 16 forwardly onto the shelving of saidstorage location. As shown in FIG. 15D, once the storage unit 16 isfully unloaded off of the vehicle 19 and onto the shelving, the vehicle19 lowers itself slightly downward in the shaft 18 via operation of itspinion wheels, thus withdrawing the catch member 78 of the shuttle 74from the primary circular catch channel 58 of the storage unit. Thisenables rearward retraction of the extended arm 38 and deployed shuttle74, as shown in FIG. 15E. With the arm 38 retracted fully into theturret 34, the robotic storage/retrieval vehicle 19 can then travelvertically through the shaft 18 via driven operation of its pinionwheels in order to depart the storage location at which the storage unitwas just shelved, and head toward another destination in the gridstructure.

While the forgoing describes loading and unloading of storage units toand from the robotic storage/retrieval vehicles particularly at storagelocations in storage columns surrounding open vertical shafts in athree-dimensional storage grid, the described capabilities of being andto load and unload at all four sides using a singular loading/unloadingmechanism that repositions itself into an appropriate one of fourdifferent working positions, all without moving a storage unit currentlycarried on the vehicle, may be employed regardless of the particularoperating environment of that robotic storage/retrieval vehicle.Accordingly, such capabilities may be employed in any variety ofthree-dimensional storage systems in which the robotic storage/retrievalvehicles need to access locations on multiple sides of available travelpaths through said system, whether or not said travel paths arespecifically vertical shafts of a three-dimensional grid structure.

Also, while the illustrated embodiment uses a circular catch channel inthe storage bin to accommodate rotational motion of the turret of theloading/unloading mechanism while the storage unit sits stationary in astatic orientation atop the vehicle platform, other embodiments mayemploy other approaches to accommodate such relative movement of theloading/unloading mechanism into its four different working statesoperable to load/unload at the different sides of the vehicle platform.In one alternative embodiment, the catch member may be movable between araised engagement position for engagement with a catch feature in theunderside of the storage unit, and a lowered disengagement position fordisengagement from said catch feature, whereby once the storage unit isfully loaded onto the vehicle platform, the catch member is lowered intothe disengagement position, thus allowing rotation of the turret, armand shuttle relative to the storage unit seated on the deck surface.

In another alternate embodiment, instead of a ring-like circular catchchannel curving angularly about the center of the storage unit at aradial distance outward therefrom, the primary catch feature may be acentral recess centered in the underside of the storage unit floor,provided the deployed positions of the arm and shuttle are sufficient toreach this central point on the storage unit. The illustrated embodimenthas at least one advantage over such embodiments, in that since thering-like circular catch channel is located nearer to the respectiveperimeter side of the storage unit from which the vehicle is interactingtherewith, the extension/retraction distance of the vehicle arm isreduced, as can be seen in the drawings where the outward reachingdistance of the arm from the vehicle in the deployed arm position isless than half of the storage unit width. The illustrated embodiment inwhich the arm of the vehicle's loading/unloading mechanism features amoving shuttle thereon is also beneficial in maximizing the compatiblestorage unit size relative to the vehicle platform while minimizing thenecessary extension/retraction distance of the vehicle arm, though otherembodiments could employ a longitudinally fixed catch member of staticlongitudinal position on the extendable/retractable arm withoutdetriment to other novel and inventive features of the illustratedembodiment.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of samemade, it is intended that all matter contained in the accompanyingspecification shall be interpreted as illustrative only and not in alimiting sense.

The invention claimed is:
 1. In combination, a storage unit storablewithin a three-dimensional storage system and a storage/retrievalvehicle navigable through said three-dimensional storage system tostorage locations therein at which said storage unit is selectivelystorable and retrievable, wherein said storage/retrieval vehiclecomprises a frame conveyable through said three-dimensional storagesystem, a platform atop said frame for receipt of said storage unit onsaid platform, and a loading/unloading mechanism operable to load andunload said storage unit to and from said platform at four differentsides thereof, wherein said storage unit and said storage/retrievalvehicle are configured to enable unloading of the storage unit from saidplatform in any one of four different directions at four differentrespective sides of the vehicle regardless of an original orientation inwhich said storage unit was previously loaded onto the platform andwithout reorienting said storage unit from said original orientation. 2.The combination of claim 1 wherein the loading/unloading mechanism isswitchable between four different working states each operable to loadand unload said storage unit at a respective one of the four differentsides of the platform, and the storage unit and said storage/retrievalvehicle are configured to enable static support of the storage unit onsaid platform in a static orientation thereon while saidloading/unloading mechanism transitions between the different workingstates.
 3. In combination, a storage unit storable within athree-dimensional storage system and a storage/retrieval vehiclenavigable through said three-dimensional storage system to storagelocations therein at which said storage unit is selectively storable andretrievable, wherein said storage/retrieval vehicle comprises a frameconveyable through said three-dimensional storage system, a platformatop said frame for receipt of said storage unit on said platform, and aloading/unloading mechanism operable to load and unload said storageunit to and from said platform at four different sides thereof, wherein:said storage unit and said storage/retrieval vehicle are configured toenable unloading of the storage unit from said platform in any one offour different directions at four different respective sides of thevehicle regardless of an original orientation in which said storage unitwas previously loaded onto the platform and without reorienting saidstorage unit from said original orientation; said loading/unloadingmechanism of the vehicle comprises a rotatable turret installed in saidplatform to reside beneath the storage unit when loaded onto saidplatform, and an extendable arm selectively extendable from saidrotatable turret into a deployed position reaching outwardly beyond aperimeter of said platform, said turret being rotatable into a pluralityof different working positions in which the arm is extendable outwardlyfrom the turret in said different directions at said differentrespective sides of the vehicle, and said extendable arm comprises acatch member carried thereon for engagement with an underside of thestorage unit; and said storage unit comprises a catch channel residingin an underside of the storage unit and in which the catch member of theloading/unloading mechanism is selectively engageable, wherein saidcatch channel lies on a circular path along which the catch member cantraverse the catch channel during rotation of the turret while thestorage unit is seated on said platform.
 4. The combination of claim 3wherein said catch channel spans at least 270-degrees of said circularpath.
 5. The combination of claim 4 wherein said catch channel spans afull 360-degrees of said circular path.
 6. The combination of claim 3wherein said extendable arm comprises a movable shuttle that isdisplaceable back and forth along said extendable arm and on which thecatch member resides.
 7. The combination of claim 3 wherein saidplatform comprises outer deck surfaces disposed around the turret, andthe turret resides in recessed elevation relative to said outer decksurfaces.
 8. The combination of claim 3 wherein the storage unitcomprises at least one redundant catch feature recessed in the undersidethereof at a distance situated outwardly from the circular path of thecatch channel.
 9. The combination of claim 8 wherein said at least oneredundant catch feature comprises a plurality of redundant catchrecesses each residing between the catch channel and a respective sideof the storage unit.
 10. In combination, a storage unit storable withina three-dimensional storage system and a storage/retrieval vehiclenavigable through said three-dimensional storage system to storagelocations therein at which said storage unit is selectively storable andretrievable, wherein said storage/retrieval vehicle comprises a frameconveyable through said three-dimensional storage system; a platformatop said frame for receipt of said storage unit on said platform; anextendable/retractable device that is selectively extendable into adeployed position reaching outwardly beyond a perimeter of the platformand has a catch member thereon for engagement with the storage unit inat least the deployed position of the extendable/retractable device;wherein the storage unit comprises a primary catch feature engageable bythe catch member in the deployed position of the extendable/retractabledevice during a loading operation intended to pull said storage unitonto the platform of the vehicle, and at least one secondary catchfeature positioned relative to the primary catch feature so as to beengaged by the catch member of the extendable/retractable device in amore retracted state thereof later in the loading operation should thecatch member fail to engage the primary catch feature.
 11. Thecombination of claim 10 comprising a plurality of secondary catchfeatures, each residing adjacent a respective outer perimeter side ofthe storage unit.
 12. The combination of claim 10 wherein the primaryand secondary catch features are located at an underside of the storageunit.
 13. The combination of claim 10 wherein the secondary catchfeature is recessed into the storage unit.
 14. The combination of claim10 wherein the primary catch feature is recessed into the storage unit.15. The combination of claim 10 wherein said storage/retrieval vehiclefurther comprises a rotatable turret installed in said platform, and theextendable/retractable device is selectively extendable from saidrotatable turret in each a plurality of different working positions ofsaid rotatable turret such that said extendable/retractable device canextend outward from different sides of the platform in said differentworking positions of the rotatable turret, and the primary catch featurecomprises a curved channel that resides in an underside of the storageunit and lies on a circular path along which the catch member cantraverse the curved channel during rotation of the turret while thestorage unit is seated on said platform.
 16. The combination of claim 15wherein the curved feature spans at least 270-degrees of said circularpath.
 17. The combination of claim 16 wherein said curved feature spansa full 360-degrees of said circular path.
 18. The combination of claim10 wherein the storage/retrieval vehicle comprises a set of load statussensors distributed at different locations over a landing area of theplatform and each operable to detect presence of the storage unit inoverlying relation to said sensor when said storage unit is seated onsaid landing area, wherein the extendable/retractable device isconfigured to retract a predetermined distance that is sufficient topull the storage unit fully into the landing area of the platform if theprimary catch feature was engaged, and wherein the combination furthercomprises a processor configured to query the set of load status sensorsafter retraction of the extendable/retractable device by saidpredetermined distance, and based on said query, identify either asuccessful loading of the storage unit onto the landing area based on apositive detection signal from all of said load sensors, or a failed orincomplete loading of the storage unit onto the landing area based on alack of positive detection signal from one or more of said load sensors.19. The combination of claim 18 wherein said predetermined distance issufficient to pull the storage unit partially onto the platform if thesecondary catch feature was engaged, and receipt of the positivedetection signal from a partial subset of said load sensors afterretraction of the extendable/retractable device by said predetermineddistance identifies failed engagement of the primary catch feature,successful engagement of the secondary catch feature, and partialloading of the storage unit onto the platform.
 20. The combination ofclaim 19 wherein, the processor is configured to, after detection ofsaid failed engagement of the primary catch feature and said partialloading of the storage unit, partially re-deploy theextendable/retractable device and thereby push the partially loadedstorage unit off the platform.
 21. The combination of claim 20 whereinthe processor is configured to, after partial re-deployment of theextendable/retractable device and pushing of the partially loadedstorage unit off the platform, re-attempt loading of the storage unitonto the platform via engagement of the primary catch feature by thecatch member.